Piezoelectric pressure transducers have a crystal resonator located inside a housing with electrodes. Environmental pressure and temperature are transmitted to the resonator, via the housing, and changes in the resonator are sensed and used to interpret the pressure and/or temperature. U.S. Pat. No. 3,617,780 discloses one example of pressure transducer having a quartz crystal resonator with single-mode oscillation. The quartz resonator is affected by both temperature and pressure such that some devices may not be suitable for use in environments where both temperature and pressure vary. U.S. Pat. Nos. 4,419,600, 4,547,691 and 5,394,345 disclose examples of pressure transducers having a quartz dual mode resonator. In the dual-mode resonator, B-mode vibration is primarily only responsive to temperature whereas C-mode vibration is responsive to both temperature and pressure. Thus, by noting the change in frequency in both modes, temperature and pressure can be measured simultaneously.
Many advances in the science of quartz pressure/temperature transducers have been made in connection with oil field applications. Transient or dynamic pressure measurements are routinely employed in the estimation of formation permeability, reservoir pressure, formation continuity, and reservoir boundaries. The pressures encountered during such the estimation can be greater than 20,000 psi. While making measurements, the transducers can be subjected to temperatures of approximately 175° C. or more over. In addition, a subterranean tool with a pressure transducer is connected to equipment on the ground surface via a telecommunication cable and operated under the ground in relatively long operation time. In such oil field applications, there is a need for improved pressure transducers that are capable of measuring pressure more stably and accurately in high temperature and pressure environment with low power consumption.
As will become apparent from the following description and discussion, the present invention provides an improved pressure transducer capable of operating stably and accurately in high temperature and pressure environment with low power consumption.